From the recent 'genome-wide association studies' we have to conclude that the involvement of the primary DNA sequence does not explain the full genetic predisposition of essential hypertension (EH). A more thorough understanding of additional mechanisms potentially involved in EH is a prerequisite to prevention and development of novel therapies. Changes in DNA methylation (i.e., epigenetic modification of genetic information) can play an important regulatory role (by influencing transcription) in both normal and pathological cellular processes. Based on many recent studies that highlight the involvement of inflammation in the development of EH, we hypothesize that changes in DNA methylation of leukocytes are involved in the pathogenesis of EH. We aim to identify these differentially methylation sites using a multi-step genome wide approach. First, we will identify the CpG sites where DNA methylation differs between EH cases and controls (aim 1). We will employ a step-wise selection process involving 3 stages. After interrogation of 27,000 methylation sites in more than 14,000 genes in 100 monozygotic twin pairs discordant for EH (the the ideal experimental model for identifying disease related epigenetic signals) and 100 age and gender matched external controls selected from the Finnish Twin Cohort Study, we will choose the most promising for validation and replication in 500 EH cases and 500 healthy controls. Then, we will determine whether changes in methylation of these CpG sites are associated with changes in gene expression in the cells. Functional in vitro experiments will also be conducted to investigate whether demethylation of these CpG sites can activate gene expression, which will eventually leading to the (approximately) 20 most important sites. Next, we will determine the temporal relationship between DNA methylation status and EH in a nested case-control setting (380 newly developed EH cases and 380 controls) involving assessment of methylation status at baseline and EH status after 4 years follow-up (aim 2). Furthermore, we will determine the effect of DNA methylation status on blood pressure development in the BP stress cohort which has measured BP 8 times in 299 Caucasian adolescents during 11 years follow up (aim 3). Secondary specific aim will test whether the methylation sites identified in Caucasians are also involved in the pathogenesis of EH in African Americans in the Jackson Heart Study and the BP stress cohort. We expect to pinpoint specific methylation sites likely to be involved in the pathophysiology of EH. These results might play a key role in the development of new therapeutic targets for early risk stratification and intervention.